Create a function for line graph values?

[dsochor]

In the attached Mathcad prime 3.1 worksheet (along with screenshot) I've graphed two vectors in an X-Y plot. Is it possible to create a function such that the user can type in any value for temperature( within the highest and lowest value) and receive the temperature back?

[LucMeekes · Accepted solution]

Yes, that function is

GetTemp(Temp):=Temp

You call the function with, e.g.

GetTemp(15)=

and it results in

GetTemp(15)=15.

That's what you asked, but not what you meant to ask....

I'm afraid you want a function where you give an Ec value, and get the correcponding temperature. That is partially possible.

I think the answer to your question lies with the function linterp(), look it up in the help, and see how it works.

The problem is that there is a temperature range where the Ec value is 1. What temperature would you expect to get for Ec=1?

Success!
Luc

[LucMeekes]

Here's an example using linterp().

Note that it works because there is a one-to-one relation between Temp and Ec values. If that is not the case (as in your example where Ec=1 on a range of Temp values), the linterp() funtion will complain. In that case using spline functions (see the answer below) may (...) help.

Success!

Luc

[rgunwaldsen]

Mathcad provides a variety of methods for fitting functions to data. 

Attached worksheet fits cubic spline to your data.

[dsochor]

Thank you rgunwaldsen. What format (or version) is your worksheet; I'm unable to open it.

[rgunwaldsen]

I used Prime 5. PTC has made it impossible to copy/paste stuff into prior versions of Prime.

Attached is "xps" printout.

The functions used are straight out of the help example for "Example: Cubic Spline Interpolation

Example: Cubic Spline Interpolation".

Advantage for cubic spline fit for interpolation within range is that it provides "smooth" function with continuity of function and 1st/2nd derivatives.

Roger

[Werner_E]

My guess is that you want a function to calculate Ec from a given temp and not the other way round.

If linear interpolation is sufficient you may do like this: